George Zimmerman stands during jury selection in his trial in Seminole circuit court in Sanford, Fla. / Gary Green, AP

by Yamiche Alcindor, USA TODAY

by Yamiche Alcindor, USA TODAY

SANFORD, Fla. - In its opening statement in the Travyon Martin murder trial, the prosecution Monday portrayed defendant George Zimmerman as a trigger-happy, policeman wannabe who saw the teenager as a suspicious person and considered it his right to "rid the neighborhood of anyone that he believed didn't belong."

"The truth about the murder of Trayvon Martin is going to come directly from his mouth, from those hate-filled words that he used to describe a perfect stranger and from the lies that he told to the police to try to justify his actions," prosecutor John Guy told the six-woman jury.

Guy moved quickly to try to jolt the jurors by using the "f-word" followed by "punks" in quoting from Zimmerman's conversation by cellphone with a police dispatcher as he followed the unarmed teenager.

Zimmerman's defense attorney Don West countered that the neighborhood watch volunteer shot Trayvon in self-defense after he was viciously attacked by the 17-year-old Miami-area teen.

Zimmerman, 29, has pleaded not guilty to second-degree murder in the fatal shooting of Trayvon on Feb. 26, 2012, at the gated community where Trayvon's father lived.

A 911 call that recorded screaming and the gunshot will be a key part of the trial. However, Circuit Judge Debra Nelson ruled Saturday that prosecution experts who said the voice screaming was Trayvon's will not be allowed to testify. Witnesses familiar with the voices of Zimmerman and Trayvon can testify to whom they believe is screaming, the judge ruled. That means Trayvon's and Zimmerman's families may testify.

In his opening statement, prosecutor Guy called the killing a "product of two worlds colliding."

One world, he said, was a boy visiting his father and walking home after buying a fruit drink and Skittles at a local convenience store.

In the other world, the prosecutor said, was a (then) 28-year-old adult, a neighborhood watch coordinator, who was patrolling the area at night with a semiautomatic pistol tucked in his waistband in a "ready-to-fire position" with one live round in the chamber.

"When he saw Trayvon Martin, he didn't see a young man walking home," the prosecutor said. "As he told the (police) dispatcher, he saw someone that was 'real suspicious,' someone who looked like he was 'up to no good,' again, to use his word."

The prosecutor noted that in his conversation on a cellphone with the police dispatcher, he made the comments that "these a--holes, they always get away."

In explaining the state's case against Zimmerman, Guy, often pointing directly at Zimmerman, repeated those words several times saying Zimmerman wrongly profiled a teen walking home as a criminal.

"Those words were in his chest," Guy said. "Those words were in the defendant's heart before he pressed a pistol to Trayvon Martin's chest."

Guy said Zimmerman had spun a web of lies when he said Trayvon punched him, and knocked him down.

West, however, told jurors that Trayvon had thrown a "sucker punch" at Zimmerman after possibly hiding. "Trayvon Martin decided to confront George Zimmerman,'' West said. "The evidence will show this is a sad case,'' he said. "There are no monsters."

West began his opening statement with a joke. "Knock, knock," West said. "Who's there? George Zimmerman. George Zimmerman who? All right good, you're on the jury."

The court remained quiet and jurors' faces were blank. Later, after a break, West promised not to tell any more bad jokes.

Guy said earlier that police officers on the scene, emergency personnel, a medical examiner and several residents who live nearby the shooting will testify.

"No one heard or saw this from start to beginning to end," said Guy, explaining that witnesses saw slices that don't fit with Zimmerman's version.

The state will also show evidence that Zimmerman applied to be a police officer, wanted to go on a police ride, was a criminal justice student and initiated a neighborhood watch program as captain, Guy said.

He added that at least a year before the shooting Zimmerman was taking martial arts and self-defense classes at a gym and learning how to fight.

Guy pointed out that none of Zimmerman's blood or DNA was found on Trayvon's body, clothing, or under his nails. Zimmerman's gun also didn't have any of Trayvon's blood or DNA, he said.

Guy said medical personnel tried to save Trayvon who was found facedown with his hands on his chest. Photos of Trayvon will be shown to the jury.

He said the jury will hear the 911 call and that the screaming stops instantly when the gun goes off.

"George Zimmerman did not shoot Trayvon Martin because he had to," Guy said. "He shot him for the worst of all reasons - because he wanted to."

Prosecutors called four witnesses to the stand Monday afternoon. The first was Chad Joseph, 15, son of Trayvon's father's girlfriend.

He testified that he and Trayvon spent the day playing video games and watching television on Feb. 26, 2012. He said Trayvon later left for the convenience store and that Chad didn't go because he was paying video games with headphones on.

He said he called Trayvon while he was gone and that Trayvon said he was on his way back but never arrived. Chad never saw or heard from Trayvon again.

Shortly before opening statements, the family of Trayvon Martin and their attorney asked for prayers.

"As the court proceedings continue, we as a family look and cherish the memories that Trayvon left us with," said Trayvon's father, Tracy Martin, adding that memories of his son's smile gave him strength.

The teen's mother, who remained quiet during two weeks of jury selection, also spoke.

"I don't want any other mother to have to experience what I'm going through now," Sybrina Fulton said. "I ask that you pray for me and my family."

Fulton said she plans to attend the trial every day to offer support for her son's memory.

Trayvon's brother, Jahvaris Fulton, as well as the late teen's grandmother also attended proceedings.

The family's attorney, Benjamin Crump, said while murder trials are emotional, the jury will need to do its duty and listen to all the facts.

"There are two important facts in this case," Crump said. "George Zimmerman was a grown man with a gun. Trayvon Martin was a minor with no blood on his hands."

Nelson, honoring a prosecution request, ordered Zimmerman's family to leave the courtroom for the duration of the trial because members are potential witnesses.

In a statement to the media, Robert Zimmerman, George's brother, was critical of the move. He said George "can count on his parents' & his family's unwavering & unconditional support, as he has throughout this ordeal, until he is acquitted."

Trayvon's family can stay because Florida law allows the victim's family to stay.

Benjamin Crump, an attorney for Trayvon Martin's family, however, cannot attend the trial because he too is a potential witness.